Download Infectious diseases of potential risk for travellers

CHAPTER 5. INFECTIOUS DISEASES OF POTENTIAL RISK FOR TRAVELLERS
CHAPTER 5
Infectious diseases of
potential risk for travellers
Depending on the travel destination, travellers may be exposed to a number of
infectious diseases; exposure depends on the presence of infectious agents in the area
to be visited. The risk of becoming infected will vary according to the purpose of
the trip and the itinerary within the area, the standards of accommodation, hygiene
and sanitation, as well as the behaviour of the traveller. In some instances, disease
can be prevented by vaccination, but there are some infectious diseases, including
some of the most important and most dangerous, for which no vaccines exist.
General precautions can greatly reduce the risk of exposure to infectious agents
and should always be taken for visits to any destination where there is a significant
risk of exposure. These precautions should be taken regardless of whether any
vaccinations or medication have been administered.
Modes of transmission and general precautions
The modes of transmission for different infectious diseases and the corresponding
general precautions are outlined in the following paragraphs.
Foodborne and waterborne diseases
Foodborne and waterborne diseases are transmitted by consumption of contaminated food and drink. The risk of infection is reduced by taking hygienic
precautions with all food, drink and drinking-water consumed when travelling
and by avoiding direct contact with polluted recreational waters (see Chapter 3).
Examples of diseases acquired by food and water consumption are traveller’s
diarrhoea, hepatitis A, typhoid fever and cholera.
Vector-borne diseases
A number of particularly serious infections are transmitted by insects and other
vectors such as mosquitoes and ticks. The risk of infection can be reduced by
taking precautions to avoid insect bites and contact with other vectors in places
where infection is likely to be present (see Chapter 3). Examples of vector-borne
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diseases are malaria, yellow fever, dengue, Japanese encephalitis, chikungunya and
tick-borne encephalitis.
Zoonoses (diseases transmitted by animals)
Zoonoses include many infections that can be transmitted to humans through
animal bites or contact with animals, contaminated body fluids or faeces, or by
consumption of foods of animal origin, particularly meat and milk products. The
risk of infection can be reduced by avoiding close contact with any animals—including wild, captive and domestic animals—in places where infection is likely to
be present. Particular care should be taken to prevent children from approaching
or touching animals. Examples of zoonoses are rabies, tularemia, brucellosis,
leptospirosis and certain viral haemorrhagic fevers.
Sexually transmitted diseases
Sexually transmitted diseases are passed from person to person through unsafe
sexual practices. The risk of infection can be reduced by avoiding casual and
unprotected sexual intercourse, and by use of condoms. Examples of sexually
transmitted diseases are hepatitis B, HIV/AIDS and syphilis.
Bloodborne diseases
Bloodborne diseases are transmitted by direct contact with infected blood or other
body fluids. The risk of infection can be reduced by avoiding direct contact with
blood and body fluids, by avoiding the use of potentially contaminated needles
and syringes for injection or any other medical or cosmetic procedure that penetrates the skin (including acupuncture, piercing and tattooing), and by avoiding
transfusion of unsafe blood (see Chapter 8). Examples of bloodborne diseases are
hepatitis B and C, HIV/AIDS and malaria.
Airborne diseases
Airborne transmission occurs when droplet nuclei (evaporated droplets) < 5 micron
in size are disseminated in the air. These droplet nuclei can remain suspended in the
air for some time. Droplet nuclei are the residuals of droplets and when suspended
in the air, they dry and produce particles ranging in size from 1–5 microns. Diseases
spread by this mode include open/active pulmonary tuberculosis (TB), measles,
chicken pox, pulmonary plague and haemorrhagic fever with pneumonia.
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Droplet transmission occurs when there is adequate contact between the mucous
membranes of the nose and mouth or conjunctivae of a susceptible person and
large particle droplets (> 5 microns). Droplets are usually generated by the infected
person during coughing, sneezing, talking or when health care workers undertake
procedures such as tracheal suctioning. Diseases transmitted by this route include
pneumonias, pertussis, diphtheria, SARS, mumps and meningitis.
Diseases transmitted from soil
Soil-transmitted diseases include those caused by dormant forms (spores) of
infectious agents, which can cause infection by contact with broken skin (minor cuts, scratches, etc). The risk of infection can be reduced by protecting the
skin from direct contact with soil in places where soil-transmitted infections
are likely to be present. Examples of bacterial diseases transmitted from soil are
anthrax and tetanus. Certain intestinal parasitic infections, such as ascariasis and
trichuriasis, are transmitted via soil and infection may result from consumption
of soil-contaminated vegetables. Fungal infections may be acquired by inhalation
of contaminated soil.
Specific infectious diseases involving potential health risks
for travellers
The main infectious diseases to which travellers may be exposed, and precautions
for each, are detailed on the following pages. Information on malaria, one of the
most important infectious disease threats for travellers, is provided in Chapter 7.
The infectious diseases described in this chapter have been selected on the basis
of the following criteria:
— diseases that have a sufficiently high global or regional prevalence to constitute a significant risk for travellers;
— diseases that are severe and life-threatening, even though the risk of exposure
may be low for most travellers;
— diseases for which the perceived risk may be much greater than the real
risk, and which may therefore cause anxiety to travellers;
— diseases that involve a public health risk due to transmission of infection
to others by the infected traveller.
Information about available vaccines and indications for their use by travellers is
provided in Chapter 6. Advice concerning the diseases for which vaccination is
routinely administered in childhood, i.e. diphtheria, measles, mumps and rubella,
pertussis, poliomyelitis and tetanus, and the use of the corresponding vaccines later
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in life and for travel, is also given in Chapter 6. These diseases are not included
in this chapter.
The most common infectious illness to affect travellers, namely travellers’ diarrhoea, is covered in Chapter 3. Because travellers’ diarrhoea can be caused by many
different foodborne and waterborne infectious agents, for which treatment and
precautions are essentially the same, the illness is not included with the specific
infectious diseases.
Some of the diseases included in this chapter, such as brucellosis, HIV/AIDS,
leishmaniasis and tuberculosis, have prolonged and variable incubation periods.
Clinical manifestations of these diseases may appear long after the return from
travel, so that the link with the travel destination where the infection was acquired
may not be readily apparent.
AVIAN INFLUENZA
Cause
Highly pathogenic avian influenza A(H5N1) virus, or other non-human
influenza subtypes (e.g.H7, H9).
Transmission
Human infections with highly pathogenic avian influenza A(H5N1) virus occur
through bird-to-human, possibly environment-to-human, and very rarely
limited, non-sustained human-to-human transmission. Direct contact with
infected poultry, or surfaces and objects contaminated by their droppings,
is the main route of transmission to humans. Exposure risk is considered
highest during slaughter, de-feathering, butchering, and preparation of poultry
for cooking. There is no evidence that properly cooked poultry or poultry
products can be a source of infection.
Nature of disease
Patients usually present initially with symptoms of fever and influenza-like
illness (malaise, myalgia, cough, sore throat). Diarrhoea and other gastrointestinal symptoms may occur. The disease progresses within days and
almost all patients develop clinically apparent pneumonia with radiographic
infiltrates of varying patterns. Sputum production is variable and sometimes bloody. Multi-organ failure, sepsis-like syndromes, and uncommonly
encephalopathy, occur. The fatality rate among hospitalized patients with
confirmed H5N1 infection has been high (about 60%), most commonly as
a result of respiratory failure caused by progressive pneumonia and acute
respiratory distress syndrome.
Geographical distribution
Extensive outbreaks in poultry have occurred in parts of Asia, the Middle
East, Europe and Africa since 2003, but only sporadic human infections
have occurred to date. Continued exposure of humans to avian H5N1 viruses
increases the likelihood that the virus will acquire the necessary characteristics for efficient and sustained human-to-human transmission through either
gradual genetic mutation or reassortment with a human influenza A virus.
Between November 2003 and July 2008, nearly 400 human cases of laboratory-confirmed H5N1 infection were reported to WHO from 15 countries
in South-East and central Asia, Europe, Africa and the Middle East.
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Risk for travellers
H5N1 avian influenza is primarily a disease in birds. The virus does not
easily cross the species barrier to infect humans. To date, no traveller has
been infected. The risk of infection is increased by prolonged, close and
heavy exposure to the virus.
Prophylaxis
Neuraminidase inhibitors (oseltamivir, zanamivir) are inhibitory for the virus
and demonstrate proven efficacy in vitro and in animal studies for prophylaxis
and treatment of H5N1 infection. Studies in hospitalized H5N1 patients,
although limited, suggest that early oseltamivir treatment with oseltamivir
improves survival and given the prolonged virus replication, late intervention
with oseltamivir is also justified. Neuraminidase inhibitors are recommended
for post-exposure prophylaxis in certain exposed persons. At present WHO
does not recommend pre-exposure prophylaxis for travellers but advice may
change depending on new findings. Inactivated H5N1 vaccines for human
use have been developed and licensed in several countries but are not yet
generally available although this situation is expected to change. Some
countries are stockpiling these vaccines as a part of pandemic preparedness.
Although immunogenic, the effectiveness of these vaccines in preventing the
H5N1 infection or reducing disease severity is unknown. Currently, WHO
does not have a policy in its use.
Precautions
Travellers should avoid contact with high-risk environments in affected
countries such as live animal markets and poultry farms, any free-ranging or
caged poultry, or surfaces that might be contaminated by poultry droppings.
Travellers in affected countries should avoid contact with dead migratory birds
or wild birds showing signs of disease. Travellers should avoid consumption
of undercooked eggs, poultry or poultry products. Hand hygiene with frequent
washing or use of alcohol rubs is recommended. If exposure to persons with
suspected H5N1 illness or severe, unexplained respiratory illness occurs, travellers should urgently consult health professionals. Travellers should contact
their local health providers or national health authorities for supplementary
information.
ANTHRAX
Cause
Bacillus anthracis bacteria.
Transmission
Anthrax is primarily a disease of animals. Cutaneous infection, the most
frequent clinical form of anthrax, occurs through contact with products from
infected animals (mainly cattle, goats, sheep), such as leather or woollen
goods, or through contact with soil containing anthrax spores.
Nature of the disease
A disease of herbivorous animals that occasionally causes acute infection
in humans, usually involving the skin, as a result of contact with contaminated tissues or products from infected animals, or with anthrax spores in
soil. Untreated infections may spread to regional lymph nodes and to the
bloodstream, and may be fatal.
Geographical distribution
Sporadic cases occur in animals worldwide; there are occasional outbreaks
in central Asia and Africa.
Risk for travellers
Very low for most travellers.
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Prophylaxis
None. (A vaccine is available for people at high risk because of occupational
exposure to B. anthracis; it is not commercially available in most countries.)
Precautions
Avoid direct contact with soil and with products of animal origin, such as
souvenirs made from animal skins.
BRUCELLOSIS
Cause
Several species of Brucella bacteria.
Transmission
Brucellosis is primarily a disease of animals. Infection in people is acquired
from cattle (Brucella abortus), dogs (B. canis), pigs (B. suis), or sheep and
goats (B. melitensis), usually by direct contact with infected animals or by
consumption of unpasteurized (raw) milk or cheese.
Nature of the disease
A generalized infection with insidious onset, causing continuous or intermittent fever and malaise, which may last for months if not treated adequately.
Relapse is not uncommon after treatment.
Geographical distribution
Worldwide, in animals. It is most common in developing countries, the
Mediterranean, Middle East and Central Asia and South America.
Risk for travellers
Low for most travellers. Those visiting rural and agricultural areas may be at
greater risk. There is also a risk in places where unpasteurized milk products
are sold near tourist centres.
Prophylaxis
None.
Precautions
Avoid consumption of unpasteurized milk and milk products and direct
contact with animals, particularly cattle, goats and sheep.
CHIKUNGUNYA
Cause
Chikungunya virus – an Alphavirus (family Togaviridae).
Transmission
Chikungunya is a viral disease that is spread by mosquitoes. Two important
vectors are Aedes aegypti and Aedes albopictus which also transmit dengue
virus. These species bite during daylight hours with peak activity in the
early morning and late afternoon. Both are found biting outdoors but Ae.
aegypti will also readily bite indoors. There is no direct person-to-person
transmission.
Nature of the disease
The name “chikungunya” derives from a Kimakonde word meaning “to become
contorted” and describes the stooped appearance of sufferers with joint pain.
Chikungunya is an acute febrile illness with sudden onset of fever and joint
pains, particularly affecting the hands, wrists, ankles and feet. Most patients
recover after a few days but in some cases the joint pains may persist for
weeks, months or even longer. Other common signs and symptoms include
muscle pain, headache, rash and leukopenia. Occasional cases of gastrointestinal complaints, eye, neurological and heart complications have been
reported. Symptoms in infected individuals are often mild and the infection
may go unrecognized, or be misdiagnosed in areas where dengue occurs.
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Geographical distribution
Chikungunya occurs in sub-Saharan Africa, South-East Asia and tropical
areas of the Indian subcontinent, as well as islands in the south-western
Indian Ocean.
Risk for travellers
There is a risk for travellers in areas where chikungunya is endemic and in
areas affected by ongoing epidemics.
Prophylaxis
There are no specific anti-viral drugs and no commercial vaccine. Treatment
is directed primarily at relieving the symptoms, in particular the joint pain.
Precautions
Travellers should take precautions to avoid mosquito bites during both day
and night (see Chapter 3).
CHOLERA
Cause
Vibrio cholerae bacteria, serogroups O1 and O139.
Transmission
Infection occurs through ingestion of food or water contaminated directly
or indirectly by faeces or vomitus of infected persons. Cholera affects only
humans; there is no insect vector or animal reservoir host.
Nature of the disease
An acute enteric disease varying in severity. Most infections are asymptomatic
(i.e. do not cause any illness). In mild cases, diarrhoea occurs without other
symptoms. In severe cases, there is sudden onset of profuse watery diarrhoea
with nausea and vomiting and rapid development of dehydration. In severe
untreated cases, death may occur within a few hours due to dehydration
leading to circulatory collapse.
Geographical distribution
Cholera occurs mainly in poor countries with inadequate sanitation and lack
of clean drinking-water and in war-torn countries where the infrastructure
may have broken down. Many developing countries are affected, particularly
those in Africa and Asia, and to a lesser extent, those in central and South
America (see map).
Risk for travellers
Very low for most travellers, even in countries where cholera epidemics occur.
Humanitarian relief workers in disaster areas and refugee camps are at risk.
Prophylaxis
Cholera vaccines for use by travellers and those in occupational risk groups
are available in some countries (see Chapter 6).
Precautions
As for other diarrhoeal diseases. All precautions should be taken to avoid
consumption of potentially contaminated food, drink and drinking-water. Oral
rehydration salts should be carried to combat dehydration in case of severe
diarrhoea (see Chapter 3).
DENGUE
Cause
The dengue virus – a flavivirus of which there are four serotypes.
Transmission
Dengue is mostly transmitted by the Aedes aegypti mosquito, which bites
during daylight hours. There is no direct person-to-person transmission.
Monkeys act as a reservoir host in South-East Asia and West Africa.
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Nature of the disease
Dengue occurs in three main clinical forms:
■ Dengue fever is an acute febrile illness with sudden onset of fever, followed
by development of generalized symptoms and sometimes a macular skin
rash. It is known as “breakbone fever” because of severe muscle, joint and
bone pains. Pain behind the eyes (retro-orbital pain) may be present. The
fever may be biphasic (i.e. two separate episodes or waves of fever). Most
patients recover after a few days.
■ Dengue haemorrhagic fever has an acute onset of fever followed by other
symptoms resulting from thrombocytopenia, increased vascular permeability
and haemorrhagic manifestations.
■ Dengue shock syndrome supervenes in a small proportion of cases.
Severe hypotension develops, requiring urgent medical treatment to correct
hypovolaemia. Without appropriate hospital care, 40–50% of cases can be
fatal; with timely medical care by experienced physicians and nurses the
mortality rate can be decreased to 1% or less.
Geographical distribution
Dengue is widespread in tropical and subtropical regions of central and
South America and South and South-East Asia. Is also occurs in Oceania
and Africa (see Map). The risk is lower at altitudes above 1000 metres.
Risk for travellers
There is a significant risk for travellers in areas where dengue is endemic
and in areas affected by epidemics of dengue.
Prophylaxis
There are no specific vaccines or anti-viral treatments against dengue fever. Use of
paracetamol to bring down the fever is indicated. Aspirin, and related non-steroidal
anti-inflammatory drugs (NSAIs) such as ibuprofen should be avoided.
Precautions
Travellers should take precautions to avoid mosquito bites both during the
day and evening in areas where dengue occurs.
LYMPHATIC FILARIASIS
Cause
The parasitic disease covered is caused by nematodes of the family Filarioidea.
Though this group includes lymphatic filariasis (elephantiasis), onchocerciasis
(river blindness), loiaisis (Calabar swelling) or forms of mansonellosis, the
term filariasis is usually used to describe lymphatic filariasis caused by
W.bancrofti, B.malayi or B.timori.
Transmission
Lymphatic filariasis is transmitted through the bite of infected mosquitoes,
which introduce larval forms of the nematode during a blood meal.
Nature of the disease
■ Lymphatic filariasis is a chronic parasitic disease in which adult filaria
inhabit the lymphatic vessels, discharging microfilaria into the blood stream.
Typical manifestations in symptomatic cases include filarial fever, lymphadenitis and retrograde lymphangitis followed by chronic manifestations such as
lymphoedema, hydrocele, chyluria, tropical pulmonary eosinophilic syndrome
and in rare instances renal damage.
Geographical distribution
Lymphatic filariasis occurs throughout sub-Saharan Africa and in much of
South-East Asia, in the Pacific islands and in smaller foci in south America.
Risk for travellers generally low, unless travel involves extensive exposure to
the vectors in endemic areas.
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Prophylaxis
None.
Precautions
Avoid exposure to the bites of mosquitoes in endemic areas.
GIARDIASIS
Cause
The protozoan parasite Giardia intestinalis, also known as G. lamblia and
G. duodenalis.
Transmission
Infection usually occurs through ingestion of G. intestinalis cysts in water
(including both unfiltered drinking-water and recreational waters) or food
contaminated by the faeces of infected humans or animals.
Nature of the disease
Many infections are asymptomatic. When symptoms occur, they are mainly
intestinal, characterized by chronic diarrhoea (watery initially, then loose
greasy stools), abdominal cramps, bloating, fatigue and weight loss.
Geographical distribution
Worldwide.
Risk for travellers
Significant risk for travellers in contact with recreational waters used by wildlife or with unfiltered water in swimming pools, or contaminated municipal
water supplies.
Prophylaxis
None.
Precautions
Avoid eating uncooked food (especially raw fruit and vegetables) or ingesting
any potentially contaminated (i.e. unfiltered) drinking-water or recreational
water. Water can be purified by boiling for at least 5 minutes, alternatively
by filtration or chlorination.
HAEMOPHILUS MENINGITIS
Cause
Haemophilus influenzae type b (Hib) bacteria.
Transmission
Direct contact with infected persons (usually children).
Nature of the disease
Hib causes meningitis in infants and young children; it may also cause
epiglottitis, osteomyelitis, pneumonia, sepsis and septic arthritis.
Geographical distribution
Worldwide. Hib disease is most common in countries where vaccination
against Hib is not practised. It has almost disappeared in countries where
routine childhood vaccination is carried out.
Risk for travellers
A risk for unvaccinated children visiting countries where Hib vaccination is
not practised and where infection is therefore likely to be more common.
Prophylaxis
Vaccination of children (see Chapter 6).
Precautions
None.
HAEMORRHAGIC FEVERS
Haemorrhagic fevers are viral infections; important examples are Ebola and Marburg haemorrhagic fevers,
Crimean–Congo haemorrhagic fever (CCHF), Rift Valley fever (RVF), Lassa fever, Hantavirus diseases,
dengue and yellow fever.
Hantavirus diseases, dengue and yellow fever are described separately.
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Cause
Viruses belonging to several families. Ebola and Marburg belong to the
Filoviridae family; hantaviruses, CCHF and RVF belong to Bunyaviridae
family; Lassa fever belongs to Arenaviridae family and dengue and yellow
fever belong to the Flaviviridae family.
Transmission
Viruses that cause haemorrhagic fevers are transmitted by mosquitoes (dengue, yellow fever, RVF), ticks (CCHF), rodents (Hantavirus, Lassa) or bats
(Ebola, Marburg). For Ebola or Marburg viruses, humans have been infected
from contact with tissues of diseased non-human primates and other mammals, but most human infections have resulted from direct contact with the
body fluids or secretions of infected patients. Humans who become infected
with CCHF usually become infected from a tick bite, but can also acquire the
virus from direct contact with blood or other infected issues from livestock.
RVF can be acquired either by mosquito bite or by direct contact with blood
or tissues of infected animals (mainly sheep), including consumption of
unpasteurized milk. Lassa fever virus is carried by rodents and transmitted
by excreta, either as aerosols or by direct contact. Some viral haemorrhagic
fevers were amplified in hospitals by nosocomial transmission by unsafe
procedures, use of contaminated medical devices (including needles and
syringes) and unprotected exposures to contaminated body fluids.
Nature of the diseases
The haemorrhagic fevers are severe acute viral infections, usually with sudden onset of fever, malaise, headache and myalgia followed by pharyngitis,
vomiting, diarrhoea, skin rash and haemorrhagic manifestations. The outcome
is fatal in a high proportion of cases (over 50%).
Geographical distribution
Diseases in this group occur widely in tropical and subtropical regions.
Ebola and Marburg haemorrhagic fevers and Lassa fever occur in parts of
sub-Saharan Africa. CCHF occurs in the steppe regions of central Asia and
in central Europe, as well as in tropical and southern Africa. RVF occurs in
Africa and has recently spread to Saudi Arabia. Other viral haemorrhagic
fevers occur in central and South America.
Risk for travellers
Very low for most travellers. However, travellers visiting rural or forest areas
may be exposed to infection.
Prophylaxis
None (except for yellow fever).
Precautions
Avoid exposure to mosquitoes and ticks and contact with rodents or bats.
Avoid unpasteurized milk.
HANTAVIRUS DISEASES
Hantavirus diseases are viral infections; important examples are haemorrhagic fever with renal syndrome
(HFRS) and hantavirus pulmonary syndrome (HPS).
Cause
Hantaviruses, which belong to the family of Bunyaviridae.
Transmission
Hantaviruses are carried by various species of rodents; specific viruses
have particular rodent hosts. Infection occurs through direct contact with
the faeces, saliva or urine of infected rodents or by inhalation of the virus in
rodent excreta.
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Nature of the diseases
Acute viral diseases in which the vascular endothelium is damaged, leading
to increased vascular permeability, hypotension, haemorrhagic manifestations
and shock. Impaired renal function with oliguria is characteristic of HFRS.
Respiratory failure caused by acute non-cardiogenic pulmonary oedema
occurs in HPS. The outcome is fatal in up to 15% of HFRS cases and up to
50% of HPS cases.
Geographical distribution
Worldwide, in rodents.
Risk for travellers
Very low for most travellers. However, travellers may be at risk in any
environment where rodents are present in large numbers and contact may
occur.
Prophylaxis
None.
Precautions
Avoid exposure to rodents and their excreta. Adventure travellers, back-packers, campers and travellers with occupational exposure to rodents in areas
endemic for hantaviruses should take precautions to exclude rodents from
tents or other accommodation and to protect all food from contamination
by rodents.
HEPATITIS A
Cause
Hepatitis A virus, a member of the picornavirus family.
Transmission
The virus is acquired directly from infected persons by the faecal–oral route or
by close contact, or by consumption of contaminated food or drinking-water.
There is no insect vector or animal reservoir (although some non-human
primates are sometimes infected).
Nature of the disease
An acute viral hepatitis with abrupt onset of fever, malaise, nausea and
abdominal discomfort, followed by the development of jaundice a few days
later. Infection in very young children is usually mild or asymptomatic; older
children are at risk of symptomatic disease. The disease is more severe in
adults, with illness lasting several weeks and recovery taking several months;
case-fatality is greater than 2% for those over 40 years of age and 4% for
those over 60.
Geographical distribution
Worldwide, but most common where sanitary conditions are poor and the
safety of drinking-water is not well controlled (see Map).
Risk for travellers
Non-immune travellers to developing countries are at significant risk of infection. The risk is particularly high for travellers exposed to poor conditions
of hygiene, sanitation and drinking-water control.
Prophylaxis
Vaccination (see Chapter 6).
Precautions
Travellers who are non-immune to hepatitis A (i.e. have never had the disease
and have not been vaccinated) should take particular care to avoid potentially
contaminated food and water.
HEPATITIS B
Cause
Hepatitis B virus (HBV), belonging to the Hepadnaviridae.
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Transmission
Infection is transmitted from person to person by contact with infected body
fluids. Sexual contact is an important mode of transmission, but infection
is also transmitted by transfusion of contaminated blood or blood products,
or by use of contaminated needles or syringes for injections. There is also
a potential risk of transmission through other skin-penetrating procedures
including acupuncture, piercing and tattooing. Perinatal transmission may
occur from mother to baby. There is no insect vector or animal reservoir.
Nature of the disease
Many HBV infections are asymptomatic or cause mild symptoms, which are
often unrecognized in adults. When clinical hepatitis results from infection, it
has a gradual onset, with anorexia, abdominal discomfort, nausea, vomiting,
arthralgia and rash, followed by the development of jaundice in some cases.
In adults, about 1% of cases are fatal. Chronic HBV infection persists in
a proportion of adults, some of whom later develop cirrhosis and/or liver
cancer.
Geographical distribution
Worldwide, but with differing levels of endemicity. In north America, Australia, northern and western Europe and New Zealand, prevalence of chronic
HBV infection is relatively low (less than 2% of the general population) (see
Map).
Risk for travellers
Negligible for those vaccinated against hepatitis B. Unvaccinated travellers
are at risk if they have unprotected sex or use contaminated needles or
syringes for injection, acupuncture, piercing or tattooing. An accident or
medical emergency requiring blood transfusion may result in infection if the
blood has not been screened for HBV. Travellers engaged in humanitarian
relief activities may be exposed to infected blood or other body fluids in
health care settings.
Prophylaxis
Vaccination (see Chapter 6).
Precautions
Adopt safe sexual practices and avoid the use of any potentially contaminated
instruments for injection or other skin-piercing activity.
HEPATITIS C
Cause
Hepatitis C virus (HCV), which is a hepacivirus
Transmission
The virus is acquired through person-to-person transmission by parenteral
routes. Before screening for HCV became available, infection was mainly
transmitted by transfusion of contaminated blood or blood products. Nowadays transmission frequently occurs through use of contaminated needles,
syringes and other instruments used for injections and other skin-piercing
procedures. Sexual transmission of hepatitis C occurs rarely. There is no
insect vector or animal reservoir for HCV.
Nature of the disease
Most HCV infections are asymptomatic. In cases where infection leads to
clinical hepatitis, the onset of symptoms is usually gradual, with anorexia,
abdominal discomfort, nausea and vomiting, followed by the development of
jaundice in some cases (less commonly than in hepatitis B). Most patients
will develop a long-lasting chronic infection, which may lead to cirrhosis
and/or liver cancer.
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Geographical distribution
Worldwide, with regional differences in levels of prevalence.
Risk for travellers
Travellers are at risk if they practise unsafe behaviour involving the use of
contaminated needles or syringes for injection, acupuncture, piercing or
tattooing. An accident or medical emergency requiring blood transfusion
may result in infection if the blood has not been screened for HCV. Travellers
engaged in humanitarian relief activities may be exposed to infected blood
or other body fluids in health care settings.
Prophylaxis
None.
Precautions
Adopt safe sexual practices and avoid the use of any potentially contaminated
instruments for injection or other skin-piercing activity.
HEPATITIS E
Cause
Hepatitis E virus, which has not yet been definitively classified (formerly
classified as a member of the Caliciviridae).
Transmission
Hepatitis E is a waterborne disease usually acquired from contaminated
drinking-water. Direct faecal–oral transmission from person to person is also
possible. There is no insect vector. Hepatitis E virus has a domestic animal
reservoirs host, such as pigs.
Nature of the disease
The clinical features and course of the disease are generally similar to those
of hepatitis A. As with hepatitis A, there is no chronic phase. Young adults
are most commonly affected. In pregnant women, there is an important
difference between hepatitis E and hepatitis A. During the third trimester of
pregnancy, hepatitis E takes a much more severe form with a case-fatality
rate reaching 20%.
Geographical distribution
Worldwide. Most cases, both sporadic and epidemic, occur in countries with
poor standards of hygiene and sanitation.
Risk for travellers
Travellers to developing countries may be at risk when exposed to poor
conditions of sanitation and drinking-water control.
Prophylaxis
None.
Precautions
Travellers should follow the general conditions for avoiding potentially
contaminated food and drinking-water (see Chapter 3).
HIV/AIDS AND OTHER SEXUALLY TRANSMITTED INFECTIONS
The most important sexually transmitted diseases and infectious agents are:
HIV/AIDS
human immunodeficiency virus
hepatitis B
hepatitis B virus
syphilis
Treponema pallidum
gonorrhoea
Neisseria gonorrhoeae
chlamydial infections
Chlamydia trachomatis
trichomoniasis
Trichomonas vaginalis
chancroid
Haemophilus ducreyi
genital herpes
herpes simplex virus (human (alpha) herpesvirus 2)
genital warts
human papillomavirus
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Travel restrictions
Some countries have adopted entry and visa restrictions for people with HIV/AIDS. Travellers who are
infected with HIV should consult their personal physician for a detailed assessment and advice before
travel. WHO has taken the position that there is no public health justification for entry restrictions that
discriminate solely on the basis of a person’s HIV status.
Transmission
Infection occurs during unprotected sexual intercourse (both heterosexual and
homosexual – anal, vaginal or oral). Some of these infections, such as HIV
infection, hepatitis B and syphilis can also be passed on from an infected
mother to her unborn or newborn baby and can be transmitted via blood
transfusions. Hepatitis B and HIV infections may also be transmitted through
contaminated blood products, syringes and needles used for injection, and
potentially by unsterilized instruments used for acupuncture, piercing and
tattooing.
Nature of the diseases
A number of the most common sexually transmitted infections could be
included in the following syndromes: genital ulcer, pelvic inflammatory
disease, urethral discharge and vaginal discharge. However, many infections
are asymptomatic.
Sexually transmitted infections may cause acute and chronic illness, infertility, long-term disability and death, with severe medical and psychological
consequences for millions of men, women and children.
Apart from being serious diseases in their own right, sexually transmitted
infections increase the risk of contracting or transmitting HIV infection.
Other viral infections, such as herpes simplex virus type 2 causing genital
ulcer or human papillomavirus causing cervical cancer are becoming more
prevalent. The presence of an untreated disease (ulcerative or non-ulcerative)
can increase by a factor of up to 10 the risk of becoming infected with HIV.
Individuals with HIV infection are also more likely to transmit the infection
to their sexual partner if they have a sexually transmitted infection. Early
diagnosis and treatment of all sexually transmitted infections are therefore
important.
Geographical distribution
The regional differences in the prevalence of HIV infection are shown in the
map. Sexually transmitted infections have been known since ancient times;
they remain a major public health problem, which was compounded by the
appearance of HIV/AIDS around 1980. An estimated 340 million episodes
of curable sexually transmitted infections (chlamydial infections, gonorrhoea,
syphilis, trichomoniasis) occur throughout the world every year.
Risk for travellers
For some travellers there may be an increased risk of infection. Lack of
information about risk and preventive measures and the fact that travel and
tourism may enhance the probability of having sex with casual partners
increase the risk of contracting sexually transmitted infections. In some
countries, a large proportion of sexually transmitted infections now occur
as a result of unprotected sexual intercourse during international travel.
There is no risk of acquiring any sexually transmitted infection from casual
day-to-day contact at home, at work or socially. People run no risk of infection
when sharing any means of communal transport (e.g. aircraft, boat, bus,
car, train) with infected individuals. There is no evidence that HIV or other
sexually transmitted infections can be acquired from insect bites.
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Prophylaxis
Vaccination against hepatitis B (see Chapter 6). Preventive vaccines against
oncogenic types of human papillomavirus are now available in some countries. For post-exposure prophylaxis see Chapter 8.
Precautions
The risk of acquiring a sexually transmitted infection can be prevented by
abstinence from sex with occasional or causal partners during travel or reduced by safer sexual practices such as non penetrative sex and correct and
consistent use of male or female condoms. Condoms also reduce the risk of
unwanted pregnancy. Latex rubber condoms are relatively inexpensive, are
highly reliable and have virtually no side-effects. Studies on serodiscordant
couples (only one of whom is HIV-positive) have shown that, with regular
sexual intercourse over a period of two years, partners who consistently use
condoms have a near-zero risk of HIV infection.
A man should always use a condom during sexual intercourse, each time,
from start to finish, and a woman should make sure that her partner uses
one. A woman can also protect herself from sexually transmitted infections
by using a female condom – essentially, a vaginal pouch – which is now
commercially available in some countries.
It is essential to avoid injecting drugs for non-medical purposes, and particularly to avoid any type of needle-sharing to reduce the risk of acquiring
hepatitis B and HIV infections. Blood transfusions should be given only
with a good indication to minimize the risk of transmitting infections such
as syphilis, HIV and hepatitis B infections.
Medical injections, dental care or the use of needles or blades for piercing and
tattooing using unsterilized equipment are also a possible source of infection
and should be avoided. If an injection is needed, the traveller should try to
ensure that single use needles and syringes come from a sterile package
Patients under medical care who require frequent injections, e.g. diabetics,
should carry sufficient sterile needles and syringes for the duration of their
trip and a doctor’s authorization for their use.
INFLUENZA
Cause
Influenza viruses of types A and B are associated with the epidemics and
outbreaks typical of influenza “seasons.” Influenza type C is thought to be
associated primarily with milder common cold-like illnesses. Type A viruses
are further subdivided into subtypes (H1N1 and H3N2). During an influenza
season, one of the two influenza A subtypes or influenza B can be predominant, while in other years all three viruses may be found.
Influenza viruses undergo rapid genetic evolution which eventually results
in changes to the virus’ antigenic characteristics’. Influenza vaccine virus
strains are selected each year to make sure that the vaccine is matched as
closely as possible to the currently circulating influenza strains.
Other subtypes of influenza A viruses occur in animals and all 16 HA and
9 NA subtypes are found in birds (mainly in water fowl); inter-species transmission (1918 pandemic) and viral reassortment (1957, 1968 pandemics)
may give rise to new subtypes able to infect and easily transmissible between
humans and cause the next pandemic.
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Transmission
Respiratory transmission occurs mainly by droplets disseminated by
unprotected coughs and sneezes. Short-distance airborne transmission of
influenza viruses may occur, particularly in crowded enclosed spaces. Hand
contamination and direct inoculation of virus is another possible source of
transmission.
Nature of the disease
An acute respiratory infection of varying severity, ranging from asymptomatic infection to fatal disease. Typical influenza symptoms include fever
with abrupt onset, chills, sore throat, non-productive cough and, often
accompanied by headache, coryza, myalgia and prostration. Complications
of Influenza viral infection include: primary influenza viral pneumonitis,
bacterial pneumonia, otitis media and exacerbation of underlying chronic
conditions. Illness tends to be most severe in the elderly and in infants and
young children, and in immunocompromised hosts. Death resulting from
seasonal influenza occurs mainly in the elderly and in individuals with preexisting chronic diseases.
Geographical distribution
Worldwide. In temperate regions, influenza is a seasonal disease occurring
typically in winter months: it affects the northern hemisphere from November
to April and the southern hemisphere from April to September. In tropical
areas there is no clear seasonal pattern, and influenza circulation is year
around typically with several peaks during rainy seasons.
Risk for travellers
Travellers, like local residents, are at risk in any country during the influenza
season. In addition, groups of travellers that include persons from areas
affected by seasonal influenza (e.g. cruise ships) may experience out-ofseason outbreaks. Travellers visiting countries in the opposite hemisphere
during the influenza season are at special risk, particular if they do not have
some degree of immunity through recent infection or regular vaccination.
The elderly, people with pre-existing chronic diseases and young children
are most susceptible to complications.
Prophylaxis
Vaccination before the start of the influenza season. However, vaccine for
visitors to the opposite hemisphere may not be obtainable before arrival at
the travel destination (see Chapter 6).
For travellers in the highest risk groups for severe influenza who have not
been or cannot be vaccinated, the prophylactic use of antiviral drugs such as
zanamivir or oseltamivir is indicated in countries where they are available.
Amantadine and rimantadine may also be considered when the circulating
strains are known to be susceptible. However, the latter drugs are not active
against influenza B, and high frequencies of resistance in H3N2 and less
often H1N1 viruses make then unreliable for prevention currently.
Precautions
68
Whenever possible, avoid crowded enclosed spaces and close contact with
people suffering from acute respiratory infections. Hand-washing after direct
contact with ill persons or their environment may reduce the risk of illness.
Ill persons should be encouraged to practise cough etiquette (maintain distance, cover coughs and sneezes with disposable tissues or clothing, wash
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CHAPTER 5. INFECTIOUS DISEASES OF POTENTIAL RISK FOR TRAVELLERS
JAPANESE ENCEPHALITIS
Cause
Japanese encephalitis (JE) virus, which is a flavivirus.
Transmission
The virus is transmitted by various mosquitoes of the genus Culex. It infects
pigs and various wild birds as well as humans. Mosquitoes become infective
after feeding on viraemic pigs or birds.
Nature of the disease
Most infections are asymptomatic. In symptomatic cases, severity varies; mild
infections are characterized by febrile headache or aseptic meningitis or encephalitis. Severe cases have a rapid onset and progression with headache, high
fever and meningeal signs. Permanent neurological sequelae are common among
survivors. Approximately 30% of severe clinical cases have a fatal outcome.
Geographical distribution
JE occurs in a number of countries in Asia (see Map) and occasionally in
northern Queensland, Australia.
Risk for travellers
Low for most travellers. Visitors to rural and agricultural areas in endemic
countries may be at risk, particularly during epidemics of JE.
Prophylaxis
Vaccination, if justified by likelihood of exposure (see Chapter 6).
Precautions
Avoid mosquito bites (see Chapter 3).
LEGIONELLOSIS
Cause
Various species of Legionella bacteria, frequently Legionella pneumophila,
serogroup I.
Transmission
Infection results from inhalation of contaminated water sprays or mists.
The bacteria live in water and colonize hot-water systems at temperatures
of 20–50 °C (optimal 35–46 °C). They contaminate air-conditioning cooling
towers, hot-water systems, humidifiers, whirlpool spas and other watercontaining devices. There is no direct person-to-person transmission.
Nature of the disease
Legionellosis occurs in two distinct clinical forms:
■ Legionnaires’ disease is an acute bacterial pneumonia with rapid onset of
anorexia, malaise, myalgia, headache and rapidly rising fever, progressing
to pneumonia, which may lead to respiratory failure and death.
■ Pontiac fever is an influenza-like illness with spontaneous recovery after
2–5 days.
Susceptibility to legionellosis increases with age, especially among smokers
and people with pre-existing chronic lung disease or other immunocompromising conditions.
Geographical distribution
Worldwide.
Risk for travellers
Generally low. Outbreaks occasionally occur through dissemination of infection by contaminated water or air-conditioning systems in hotels and other
facilities used by visitors.
Prophylaxis
None. Prevention of infection depends on regular cleaning and disinfection
of possible sources.
Precautions
None.
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LEISHMANIASIS (INCLUDING ESPUNDIA OR ORIENTAL SORE,
AND KALA-AZAR)
Cause
Several species of the protozoan parasite Leishmania.
Transmission
Infection is transmitted by the bite of female phlebotomine sandflies. Dogs,
rodents and other mammals are reservoir hosts for leishmaniasis. Sandflies
acquire the parasites by biting infected humans or animals. Transmission
from person to person by injected blood or contaminated syringes and needles
is also possible.
Nature of the disease
Leishmaniasis occurs in two main forms:
■ Cutaneous and mucosal leishmaniasis (espundia) causes skin sores and
chronic ulcers of the mucosae. Cutaneous leishmaniasis is generally selflimited but in a proportion of cases can be a chronic, progressive, disabling
and mutilating disease.
■ Visceral leishmaniasis (kala-azar) affects the bone marrow, liver, spleen,
lymph nodes and other internal organs. It is usually fatal if untreated.
Geographical distribution
Many countries in tropical and subtropical regions, including Africa, parts of
central and South America, Asia, southern Europe and the eastern Mediterranean. Over 90% of all cases of visceral leishmaniasis occur in Bangladesh,
Brazil, India, Nepal and Sudan. More than 90% of all cases of cutaneous
leishmaniasis occur in Afghanistan, Algeria, Brazil, the Islamic Republic of
Iran, Saudi Arabia and the Syrian Arab Republic.
Risk for travellers
Visitors to rural and forested areas in endemic countries are at risk.
Prophylaxis
None.
Precautions
Avoid sandfly bites, particularly after sunset, by using repellents and insecticide-impregnated bednets. The bite leaves a non-swollen red ring, which
can alert the traveller to its origin.
LEPTOSPIROSIS (INCLUDING WEIL DISEASE)
Cause
Various spirochaetes of the genus Leptospira.
Transmission
Infection occurs through contact between the skin (particularly skin abrasions)
or mucous membranes and water, wet soil or vegetation contaminated by the
urine of infected animals, notably rats. Occasionally infection may result from
direct contact with urine or tissues of infected animals, or from consumption
of food contaminated by the urine of infected rats.
Nature of the disease
Leptospiral infections take many different clinical forms, usually with sudden
onset of fever, headache, myalgia, chills, conjunctival suffusion and skin
rash. The disease may progress to meningitis, haemolytic anaemia, jaundice,
haemorrhagic manifestations and other complications, including hepatorenal
failure.
Geographical distribution
Worldwide. Most common in tropical countries.
Risk for travellers
Low for most travellers. There is an occupational risk for farmers engaged in
paddy rice and sugar cane production. Visitors to rural areas and in contact
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with water in canals, lakes and rivers may be exposed to infection. There
is increased risk after recent floods. The risk may be greater for those who
practise canoeing, kayaking or other activities in water. Outbreaks associated
with eco-sports activities have occurred.
Prophylaxis
Doxycycline may be used for prophylaxis if exposure is likely. Vaccine against
local strains is available for workers where the disease is an occupational
hazard, but it is not commercially available in most countries.
Precautions
Avoid swimming or wading in potentially contaminated waters including
canals, ponds, rivers, streams and swamps. Avoid all direct or indirect
contact with rodents.
LISTERIOSIS
Cause
The bacterium Listeria monocytogenes.
Transmission
Listeriosis affects a variety of animals. Foodborne infection in humans occurs
through the consumption of contaminated foods, particularly unpasteurized
milk, soft cheeses, vegetables and prepared meat products such as pâté.
Listeriosis multiplies readily in refrigerated foods that have been contaminated, unlike most foodborne pathogens. Transmission can also occur from
mother to fetus or from mother to child during birth.
Nature of the disease
Listeriosis causes meningoencephalitis and/or septicaemia in adults and
newborn infants. In pregnant women, it causes fever and abortion. Newborn
infants, pregnant women, the elderly and immunocompromised individuals
are particularly susceptible to listeriosis. In others, the disease may be
limited to a mild acute febrile episode. In pregnant women, transmission of
infection to the fetus may lead to stillbirth, septicaemia at birth or neonatal
meningitis.
Geographical distribution
Worldwide, with sporadic incidence.
Risk for travellers
Generally low. Risk is increased by consumption of unpasteurized milk and
milk products and prepared meat products.
Prophylaxis
None.
Precautions
Avoid consumption of unpasteurized milk and milk products. Pregnant women
and immunocompromised individuals should take stringent precautions to
avoid infection by listeriosis and other foodborne pathogens (see Chapter 3).
LYME BORRELIOSIS (LYME DISEASE)
Cause
The spirochaete Borrelia burgdorferi, of which there are several different
serotypes.
Transmission
Infection occurs through the bite of infected ticks, both adults and nymphs,
of the genus Ixodes. Most human infections result from bites by nymphs.
Many species of mammals can be infected, and deer act as an important
reservoir.
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Nature of the disease
The disease usually has its onset in summer. Early skin lesions have an
expanding ring form, often with a central clear zone. Fever, chills, myalgia
and headache are common. Meningeal involvement may follow. Central
nervous system and other complications may occur weeks or months after
the onset of illness. Arthritis may develop up to 2 years after onset.
Geographical distribution
There are endemic foci of Lyme borreliosis in forested areas of Asia, northwestern, central and eastern Europe, and the USA.
Risk for travellers
Generally low. Visitors to rural areas in endemic regions, particularly campers
and hikers, are at risk.
Prophylaxis
None.
Precautions
Avoid tick-infested areas and exposure to ticks (see Chapter 3). If a bite
occurs, remove the tick as soon as possible.
MALARIA
See Chapter 7 and Map.
MENINGOCOCCAL DISEASE
Cause
The bacterium Neisseria meningitidis, of which 12 serogroups are known.
Most cases of meningococcal disease are caused by serogroups A, B and
C; less commonly, infection is caused by serogroups Y (emerging in the
United States) and W-135 (particularly in Burkina Faso). Some small-scale
outbreaks caused by serogroup X have been reported in Niger and Uganda.
Epidemics in Africa are usually caused by N. meningitidis type A.
Transmission
Transmission occurs by direct person-to-person contact, and through respiratory droplets from the nose and pharynx of infected persons, patients or
asymptomatic carriers. Humans are the only reservoir.
Nature of the disease
Most infections do not cause clinical disease. Many infected people become
asymptomatic carriers of the bacteria and serve as a reservoir and source
of infection for others. In general, susceptibility to meningococcal disease
decreases with age, although there is a small increase in risk in adolescents
and young adults. Meningococcal meningitis has a sudden onset of intense
headache, fever, nausea, vomiting, photophobia and stiff neck, plus various
neurological signs. The disease is fatal in 5–10% of cases even with prompt
antimicrobial treatment in good health care facilities; among individuals who
survive, up to 20% have permanent neurological sequelae. Meningococcal
septicaemia, in which there is rapid dissemination of bacteria in the bloodstream, is a less common form of meningococcal disease, characterized by
circulatory collapse, haemorrhagic skin rash and high fatality rate.
Geographical distribution
Sporadic cases are found worldwide. In temperate zones, most cases occur in the winter months. Localized outbreaks occur in enclosed crowded
spaces (e.g. dormitories, military barracks). In sub-Saharan Africa, in a
zone stretching across the continent from Senegal to Ethiopia (the African
“meningitis belt”), large outbreaks and epidemics take place during the
dry season (November–June). Recent reports of endemic occurrence of
group Y meningococcal disease in the United States, and outbreaks cau-
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sed by serogroup W-135 strains in Saudi Arabia and sub-Saharan Africa,
particularly Burkina Faso, suggest that these serogroups may be gaining
in importance.
Risk for travellers
Generally low. However, the risk is considerable if travellers are in crowded
conditions or take part in large population movements such as pilgrimages
in the Sahel meningitis belt. Localized outbreaks occasionally occur among
travellers (usually young adults) in camps or dormitories. See also Chapter 6
for specific risks for travellers.
Prophylaxis
Vaccination is available for N. meningitidis types A, C, Y and W135 (see
Chapter 6). Protection by vaccines is group-specific, and appropriate vaccines
need to be administered to protect against the most prevalent serogroup at
the destination country of the traveller.
Precautions
Avoid overcrowding in confined spaces. Following close contact with a person
suffering from meningococcal disease, medical advice should be sought
regarding chemoprophylaxis.
ONCHOCERCIASIS
Cause
Onchocerca volvulus (a nematode)
Transmission
Onchocercias (river blindness) is transmitted through the bite of infected
blackflies.
Nature of the disease
Onchocerciasis is a chronic parasitic disease occurring mainly in subSaharan western Africa in which adult worms are found in fibrous nodules
under the skin. They discharge microfilaria, which migrate through the
skin causing dermatitis, and reach the eye causing damage that results
in blindness.
Geographical distribution
Onchocerciasis occurs mainly in western and central Africa, also in central
and South America.
Risk for travellers
Generally low, unless travel involves extensive exposure to the vectors in
endemic areas.
Prophylaxis
None.
Precautions
Avoid exposure to the bites of blackflies in endemic areas.
PLAGUE
Cause
The plague bacillus, Yersinia pestis.
Transmission
Plague is a zoonotic disease affecting rodents and transmitted by fleas
from rodents to other animals and to humans. Direct person-to-person
transmission does not occur except in the case of pneumonic plague, when
respiratory droplets may transfer the infection from the patient to others in
close contact.
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Nature of the disease
Plague occurs in three main clinical forms:
■ Bubonic plague is the form that usually results from the bite of infected
fleas. Lymphadenitis develops in the drainage lymph nodes, with the regional
lymph nodes most commonly affected. Swelling, pain and suppuration of
the lymph nodes produces the characteristic plague buboes.
■ Septicaemic plague may develop from bubonic plague or occur in the
absence of lymphadenitis. Dissemination of the infection in the bloodstream
results in meningitis, endotoxic shock and disseminated intravascular coagulation.
■ Pneumonic plague may result from secondary infection of the lungs
following dissemination of plague bacilli from other body sites. It produces
severe pneumonia. Direct infection of others may result from transfer of
infection by respiratory droplets, causing primary pulmonary plague in the
recipients.
Without prompt and effective treatment, 50–60% of cases of bubonic plague
are fatal, while untreated septicaemic and pneumonic plague are invariably
fatal.
Geographical distribution
There are natural foci of plague infection in rodents in many parts of the
world. Wild rodent plague is present in central, eastern and southern Africa,
South America, the western part of North America and in large areas of Asia.
In some areas, contact between wild and domestic rats is common, resulting
in sporadic cases of human plague and occasional outbreaks.
Risk for travellers
Generally low. However, travellers in rural areas of plague-endemic regions
may be at risk, particularly if camping or hunting or if contact with rodents
takes place.
Prophylaxis
A vaccine effective against bubonic plague is available exclusively for persons
with a high occupational exposure to plague; it is not commercially available
in most countries.
Precautions
Avoid any contact with live or dead rodents.
RABIES
Cause
The rabies virus, a rhabdovirus of the genus Lyssavirus.
Transmission
Rabies is a zoonotic disease affecting a wide range of domestic and wild
mammals, including bats. Infection of humans usually occurs through the
bite of an infected animal as the virus is present in the saliva. Any other
contact with a rabies-susceptible species such as a penetrating scratch with
bleeding and licking of broken skin and mucosa in an area where rabies is
present should be treated with caution. In developing countries, transmission
is usually through dog bites. Person-to-person transmission has not been
laboratory-confirmed.
Nature of the disease
An acute viral encephalomyelitis, which is almost invariably fatal. The
initial signs include a sense of apprehension, headache, fever, malaise and
sensory changes around the site of the animal bite. Excitability, hallucinations and aerophobia are common, followed in some cases by fear of water
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CHAPTER 5. INFECTIOUS DISEASES OF POTENTIAL RISK FOR TRAVELLERS
(hydrophobia) due to spasms of the swallowing muscles, progressing to
delirium, convulsions and death a few days after onset. A less common
form, paralytic rabies, is characterized by loss of sensation, weakness, pain
and paralysis.
Geographical distribution
Rabies is present in mammals in many countries worldwide (see Map). Most
of the estimated 55 000 rabies deaths per year in Africa and Asia alone occur
in developing countries and follow a dog bite. More information is available
on www.who.int/rabies/rabnet/en.
Risk for travellers
In rabies-endemic areas, travellers may be at risk if there is exposure to a
rabies-susceptible animal species (domestic, particularly dogs and cats, or
wild, including bats). Travellers with extensive outdoor exposure and certain
occupational activities are at higher risk even if the duration of the trip is
short. Spelunkers (cavers) should not handle bats. Children are considered
at higher risk because they may play with animals and often do not report
bites or scratches.
Prophylaxis
Vaccination for travellers with a foreseeable significant risk of exposure to
rabies or travelling to a hyperendemic area where modern rabies vaccine
may not be available (see Chapter 6).
Precautions
Avoid contact with wild animals and stray domestic animals, particularly
dogs and cats, in rabies-endemic areas. If bitten by an animal that is potentially infected with rabies, or after other suspect contact as defined above,
immediately clean the wound thoroughly with disinfectant or with soap or
detergent and water. Medical assistance should be sought immediately and
post-exposure prophylaxsis initiated if indicated (see Chapter 6).
The vaccination status of the animal involved should not be a criterion for
withholding post-exposure prophylaxis unless the vaccination has been
thoroughly documented and vaccine of known potency has been used. In
the case of domestic animals, the suspect animal should be kept under
observation for a period of 10 days. After 10 days, if the animal under
observation is healthy, post-exposure prophylaxis may be stopped.
SARS (SEVERE ACUTE RESPIRATORY SYNDROME)
Cause
SARS coronavirus (SARS-CoV) – virus identified in 2003. SARS-CoV is
thought to be an animal virus from an as–yet -uncertain animal reservoir,
perhaps bats, that spread to other animals (civet cats) ,and first infected
humans in the Guangdong province of southern China in 2002.
Transmission
An epidemic of SARS affected 26 countries and resulted in over 8000 cases
in 2003. Since then, a small number of cases have occurred as a result of
laboratory accidents or, possibly, through animal-to-human transmission
(Guangdong, China).
Transmission of SARS-CoV is primarily from person-to-person. It appears
to have occurred mainly during the second week of illness, which corresponds to the peak of virus excretion in respiratory secretions and stool, and
when cases with severe disease start to deteriorate clinically. Most cases
of human-to-human transmission occurred in the healthcare setting, in the
absence of adequate infection control precautions. The implementation of
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appropriate infection control practices brought the global outbreak to an
end.
Nature of the disease
Symptoms are flu-like and include fever, malaise, muscle aches and pains
(myalgia), headache, diarrhoea, and shivering (rigors). No individual symptom
or cluster of symptoms has proved to be specific for a diagnosis of SARS.
Although fever is the most frequently reported symptom, it is sometimes
absent on initial measurement, especially in elderly and immunosuppressed
patients.
Cough (initially dry), shortness of breath, and diarrhoea present in the first
and/or second week of illness. Severe cases often evolve rapidly, progressing
to respiratory distress and requiring intensive care.
Geographical distribution
The distribution is based on the 2002–2003 epidemic. The disease appeared
in November 2002 in the Guangdong province of southern China. This area
is considered as a potential zone of re-emergence of SARS-CoV.
Other countries/areas in which chains of human-to-human transmission
occurred after early importation of cases were Hong Kong Special Administrative Region of China and Taiwan (Province of China), Toronto in Canada,
Singapore, and Hanoi in Viet Nam.
Risk for travellers
Currently, no areas of the world are reporting transmission of SARS. Since
the end of the global epidemic in July 2003, SARS has reappeared four
times – three times from laboratory accidents (Singapore; Taiwan, Province
of China), and once in southern China where the source of infection remains
undetermined although there is circumstantial evidence of animal-to-human
transmission.
Should SARS re-emerge in epidemic form, WHO will provide guidance on
the risk of travel to affected areas. Travellers should stay informed about
current travel recommendations. However, even during the height of the
2003 epidemic, the overall risk of SARS-CoV transmission to travellers was
low.
Prophylaxis
None. Experimental vaccines are under development.
Precautions
Follow any travel recommendations and health advice issued by WHO.
SCHISTOSOMIASIS (BILHARZIASIS)
Cause
Several species of parasitic blood flukes (trematodes), of which the most
important are Schistosoma mansoni, S. japonicum, S.mekongi and S. haematobium.
Transmission
Infection occurs in fresh water containing larval forms (cercariae) of schistosomes, which develop in snails. The free-swimming larvae penetrate the
skin of individuals swimming or wading in water. Snails become infected as
a result of excretion of eggs in human urine or faeces.
Nature of the disease
Chronic conditions in which adult flukes live for many years in the veins
(mesenteric or vesical) of the host where they produce eggs, which cause
damage to the organs in which they are deposited. The symptoms depend
on the main target organs affected by the different species, with S. mansoni,
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S. mekongi and S. japonicum causing hepatic and intestinal signs and
S. haematobium causing urinary dysfunction. The larvae of some schistosomes of birds and other animals may penetrate human skin and cause a
self-limiting dermatitis, “swimmers itch”. These larvae are unable to develop
in humans.
Geographical distribution
S. mansoni occurs in many countries of sub-Saharan Africa, in the Arabian
peninsula, and in Brazil, Suriname and Venezuela. S. japonicum is found in
China, in parts of Indonesia, and in the Philippines. S. haematobium is present in sub-Saharan Africa and in eastern Mediter-ranean areas. S. mekongi
is found along the Mekong River in northern Cambodia and in the south of
the Lao People’s Democratic Republic (see Map).
Risk for travellers
In endemic areas, travellers are at risk while swimming or wading in fresh
water.
Prophylaxis
None.
Precautions
Avoid direct contact (swimming or wading) with potentially contaminated
fresh water in endemic areas. In case of accidental exposure, dry the skin
vigorously to reduce penetration by cercariae. Avoid drinking, washing, or
washing clothing in water that may contain cercariae. Water can be treated
to remove or inactivate cercariae by paper filtering or use of iodine or chlorine.
TICK-BORNE ENCEPHALITIS (SPRING–SUMMER ENCEPHALITIS)
Cause
The tick-borne encephalitis (TBE) virus is a flavivirus. Three subtypes of the
causative agent are known. The most common subtypes are the European
subtype, the Far Eastern subtype (Spring Summer encephalitis) and the
Siberian subtype. Other closely related viruses cause similar diseases.
Transmission
Infection is transmitted by the bite of infected ticks or by ingestion of unpasteurized milk. There is no direct person-to-person transmission. Some related
viruses, also tick-borne, infect animals such as birds, deer (louping-ill),
rodents and sheep.
Nature of the disease
Infection may induce an influenza-like illness, with a second phase of fever
occurring in 10% of cases. Encephalitis develops during the second phase
and may result in paralysis, permanent sequelae or death. Severity of illness
increases with age. The Far Eastern subtype causes more severe symptoms
and sequelae than the European subtype.
Geographical distribution
The European subtype is present in large parts of central and eastern Europe, particularly Austria, southern Germany or northern Switzerland, the
Baltic states (Estonia, Latvia, Lithuania), the Czech Republic, Hungary and
Poland; the Far Eastern subtype is found from north eastern Europe to China
and Japan, and the Siberian subtype from northern Europe to Siberia. The
disease is seasonal; most cases occur during April to November. The risk is
highest in forested areas up to an altitude of about 1400 m.
Risk for travellers
In endemic areas during the summer months, travellers are at risk when
hiking or camping in rural or forested areas.
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Prophylaxis
A vaccine against TBE is available (see Chapter 6).
Precautions
Avoid bites by ticks by wearing long trousers and closed footwear when hiking
or camping in endemic areas. If a bite occurs, the tick should be removed
as soon as possible.
TRYPANOSOMIASIS
1. African trypanosomiasis (sleeping sickness)
Cause
Protozoan parasites Trypanosoma brucei gambiense and T. b. rhodesiense.
Transmission
Infection occurs through the bite of infected tsetse flies. Humans are the
main reservoir host for T. b. gambiense. Domestic cattle and wild animals,
including antelopes, are the main animal reservoir of T. b. rhodesiense.
Nature of the disease
T. b. gambiense causes a chronic illness with onset of symptoms after a
prolonged incubation period of weeks or months. T. b. rhodesiense causes
a more acute illness, with onset a few days or weeks after the infected bite;
often, there is a striking inoculation chancre. Initial clinical signs include
severe headache, insomnia, enlarged lymph nodes, anaemia and rash. In the
late stage of the disease, there is progressive loss of weight and involvement
of the central nervous system. Without treatment, the disease is invariably
fatal.
Geographical distribution
T. b. gambiense is present in foci in the tropical countries of western and
central Africa. T. b. rhodesiense occurs in eastern Africa, extending south
as far as Botswana.
Risk for travellers
Travellers are at risk in endemic regions if they visit rural areas for hunting,
fishing, safari trips, sailing or other activities in endemic areas.
Prophylaxis
None.
Precautions
Travellers should be aware of the risk in endemic areas and as far as possible avoid any contact with tsetse flies. However, bites are difficult to avoid
because tsetse flies can bite through clothing. Travellers should be warned
that tsetse flies bite during the day and are not repelled by available insectrepellent products. The bite is painful, which helps to identify its origin,
and travellers should seek medical attention promptly if symptoms develop
subsequently.
2. American trypanosomiasis (Chagas disease)
Cause
Protozoan parasite Trypanosoma cruzi.
Transmission
Infection is transmitted by blood-sucking triatomine bugs (“kissing bugs”).
Oral transmission by ingestion of unprocessed freshly squeezed sugar cane
in areas where the vector is present has also been reported. During feeding,
infected bugs excrete trypanosomes, which can then contaminate the
conjunctiva, mucous membranes, abrasions and skin wounds including the
bite wound. Transmission also occurs by blood transfusion when blood has
been obtained from an infected donor. Congenital infection is possible, due
to parasites crossing the placenta during pregnancy. T. cruzi infects many
species of wild and domestic animals as well as humans.
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CHAPTER 5. INFECTIOUS DISEASES OF POTENTIAL RISK FOR TRAVELLERS
Nature of the disease
In adults, T. cruzi causes a chronic illness with progressive myocardial damage
leading to cardiac arrhythmias and cardiac dilatation, and gastrointestinal
involvement leading to mega-oesophagus and megacolon. T. cruzi causes
acute illness in children, which is followed by chronic manifestations later
in life.
Geographical distribution
American trypanosomiasis occurs in Mexico and in central and South America
(as far south as central Argentina and Chile). The vector is found mainly in
rural areas where it lives in the walls of poorly-constructed housing.
Risk for travellers
In endemic areas, travellers are at risk when trekking, camping or using
poor-quality housing.
Precautions
Avoid exposure to blood-sucking bugs. Residual insecticides can be used
to treat housing. Exposure can be reduced by the use of bednets in houses
and camps.
TUBERCULOSIS
Cause
Mycobacterium tuberculosis, the tubercle bacillus. Infection is usually by
direct airborne transmission from person to person.
Nature of the disease
Exposure to M. tuberculosis may lead to infection, but most infections do not
lead to disease. The risk of developing disease following infection is generally
5–10% during the lifetime, but may be increased by various factors, notably
immunosuppression (e.g. advanced HIV infection).
Multidrug resistance refers to strains of M. tuberculosis that are resistant
to at least isoniazid and rifampicin (MDR-TB). The resistant strains do not
differ from other strains in infectiousness, likelihood of causing disease, or
general clinical effects; however, if they do cause disease, treatment is more
difficult and the risk of death will be higher. Extensively drug-resistant TB
(XDR-TB) is TB that is resistant to at least isoniazid and rifampin, to any
fluoroquinolone and to at least one of the injectable second-line anti-TB
drugs capreomycin, kanamycin and amikacin.
Geographical distribution
Worldwide. The risk of infection differs between countries, as shown on the
map of estimated TB incidence.
Risk for travellers
Low for most travellers. Long-term travellers (over 3 months) to a country
with a higher incidence of tuberculosis than their own may have a risk of
infection comparable to that for local residents. As well as the duration of
the visit, living conditions are important in determining the risk of infection:
high-risk settings include health facilities, shelters for the homeless, and
prisons.
Prophylaxis
BCG vaccine is of limited use for travellers but may be advised for infants
and young children in some situations (see Chapter 6).
Precautions
Travellers should avoid close contact with known tuberculosis patients. For
travellers from low-incidence countries who may be exposed to infection in
relatively high-incidence countries (e.g. health professionals, humanitarian
relief workers, missionaries), a baseline tuberculin skin test is advisable in
order to compare with retesting after return. If the skin reaction to tuber-
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culin suggests recent infection, the traveller should receive, or be referred
for, treatment for latent infection. Patients under treatment for tuberculosis
should not travel until the treating physician has documented, by laboratory
examination of sputum, that the patient is not infectious and therefore of
no risk to others. The importance of completing the prescribed course of
treatment should be stressed.
TYPHOID FEVER
Cause
Salmonella typhi, the typhoid bacillus, which infects only humans. Similar
paratyphoid and enteric fevers are caused by other species of Salmonella,
which infect domestic animals as well as humans.
Transmission
Infection is transmitted by consumption of contaminated food or water.
Occasionally direct faecal–oral transmission may occur. Shellfish taken from
sewage-polluted beds are an important source of infection. Infection occurs
through eating fruit and vegetables fertilized by night soil and eaten raw, and
milk and milk products that have been contaminated by those in contact
with them. Flies may transfer infection to foods, resulting in contamination
that may be sufficient to cause human infection. Pollution of water sources
may produce epidemics of typhoid fever, when large numbers of people use
the same source of drinking-water.
Nature of the disease
A systemic disease of varying severity. Severe cases are characterized by
gradual onset of fever, headache, malaise, anorexia and insomnia. Constipation is more common than diarrhoea in adults and older children. Without
treatment, the disease progresses with sustained fever, bradycardia, hepatosplenomegaly, abdominal symptoms and, in some cases, pneumonia. In
white-skinned patients, pink spots (papules), which fade on pressure, appear
on the skin of the trunk in up to 50% of cases. In the third week, untreated
cases develop additional gastrointestinal and other complications, which
may prove fatal. Around 2–5% of those who contract typhoid fever become
chronic carriers, as bacteria persist in the biliary tract after symptoms have
resolved.
Geographical distribution
Worldwide. The disease occurs most commonly in association with poor
standards of hygiene in food preparation and handling and where sanitary
disposal of sewage is lacking.
Risk for travellers
Generally low risk for travellers, except in parts of northern and western Africa,
in southern Asia, parts of Indonesia and in Peru. Elsewhere, travellers are
usually at risk only when exposed to low standards of hygiene with respect
to food handling, control of drinking-water quality, and sewage disposal.
Prophylaxis
Vaccination (see Chapter 6).
Precautions
Observe all precautions against exposure to foodborne and waterborne
infections (see Chapter 3).
TYPHUS FEVER (EPIDEMIC LOUSE-BORNE TYPHUS)
Cause
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Rickettsia prowazekii.
CHAPTER 5. INFECTIOUS DISEASES OF POTENTIAL RISK FOR TRAVELLERS
Transmission
The disease is transmitted by the human body louse, which becomes infected
by feeding on the blood of patients with acute typhus fever. Infected lice
excrete rickettsia onto the skin while feeding on a second host, who becomes
infected by rubbing louse faecal matter or crushed lice into the bite wound.
There is no animal reservoir.
Nature of the disease
The onset is variable but often sudden, with headache, chills, high fever,
prostration, coughing and severe muscular pain. After 5–6 days, a macular
skin eruption (dark spots) develops first on the upper trunk and spreads to
the rest of the body but usually not to the face, palms of the hands or soles
of the feet. The case-fatality rate is up to 40% in the absence of specific
treatment. Louse-borne typhus fever is the only rickettsial disease that can
cause explosive epidemics.
Geographical distribution
Typhus fever occurs in colder (i.e. mountainous) regions of central and eastern
Africa, central and South America, and Asia. In recent years, most outbreaks
have taken place in Burundi, Ethiopia and Rwanda. Typhus fever occurs in
conditions of overcrowding and poor hygiene, such as prisons and refugee
camps.
Risk for travellers
Very low for most travellers. Humanitarian relief workers may be exposed
in refugee camps and other settings characterized by crowding and poor
hygiene.
Prophylaxis
None.
Precautions
Cleanliness is important in preventing infestation by body lice. Insecticidal
powders are available for body-louse control and treatment of clothing for
those at high risk of exposure.
YELLOW FEVER
Cause
The yellow fever virus, an arbovirus of the Flavivirus genus.
Transmission
Yellow fever in urban and some rural areas is transmitted by the bite of
infective Aedes aegypti mosquitoes and by other mosquitoes in the forests
of South America. The mosquitoes bite during daylight hours. Transmission
can occur at altitudes up to 2300 metres. Yellow fever virus infects humans
and monkeys.
In jungle and forest areas, monkeys are the main reservoir of infection,
with transmission from monkey to monkey carried out by mosquitoes. The
infective mosquitoes may bite humans who enter the forest area, usually
causing sporadic cases or small outbreaks.
In urban areas, monkeys are not usually involved and infection is transmitted among humans by mosquitoes. Introduction of infection into densely
populated urban areas can lead to large epidemics of yellow fever.
In Africa, an intermediate pattern of transmission is common in humid
savannah regions. Mosquitoes infect both monkeys and humans, causing
localized outbreaks.
Nature of the disease
Although most of the infections are asymptomatic and not detected, some
infections lead to an acute illness characterized by two phases. Initially, there
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is fever, muscular pain, headache, chills, anorexia, nausea and/or vomiting,
often with bradycardia. About 15% of patients progress to a second phase
after a few days, with resurgence of fever, development of jaundice, abdominal
pain, vomiting and haemorrhagic manifestations; half of these patients die
10–14 days after onset of illness.
Geographical distribution
The yellow fever virus is endemic in some tropical areas of Africa and central
and South America (see map). The number of epidemics has increased since
the early 1980s. Other countries are considered to be at risk of introduction
of yellow fever due to the presence of the vector and suitable primate hosts
(including Asia, where yellow fever has never been reported).
Risk for travellers
Travellers are at risk in all areas where yellow fever is endemic. The risk is
greatest for visitors who enter forest and jungle areas.
Prophylaxis
Vaccination (see Chapter 6). In some countries, yellow fever vaccination is
mandatory for visitors (see Country list).
Precautions
Avoid mosquito bites during the day and evening (se evening (see Chapter 3).
Further reading
Disease outbreak news: http://www.who.int/csr/don/en
Heymann D, ed. Control of communicable diseases manual, 18th ed. Washington, DC,
American Public Health Association, 2005.
Weekly epidemiological record: http://www.who.int/wer/
WHO information on infectious diseases: http://www.who.int/csr/disease/en
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